From mboxrd@z Thu Jan  1 00:00:00 1970
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Subject: Re: [kvm-unit-tests PATCH] powerpc: Add tests for RTAS
Date: Thu, 3 Mar 2016 17:03:09 +0100
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To: Laurent Vivier <lvivier@redhat.com>
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2016-03-03 13:28+0100, Laurent Vivier:
> By starting with get-time-of-day, set-time-of-day.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
> diff --git a/powerpc/rtas.c b/powerpc/rtas.c
> +#define DAYS(y,m,d) (365UL * (y) + ((y) / 4) - ((y) / 100) + ((y) / 400) + \
> +		     367UL * (m) / 12  + \
> +		     (d))

This function is hard to (re)use.
What about putting the "month -= 2" block together with DAYS to give a
better estimate of the amount of days in the gregorian calendar?

  static inline unsigned long days(int year, int month, int day) {
  	month -= 2;
  	if (month <= 0) {
  		month += 12;
  		year -= 1;
  	}
  	return DAYS(year, month, day);
  }

(Or replacing it with an obvious, but slower/bigger implementation? :])

> +	/* Put February at end of the year to avoid leap day this year */
> +
> +	month -= 2;
> +	if (month <= 0) {
> +		month += 12;
> +		year -= 1;
> +	}
> +
> +	/* compute epoch: substract DAYS(since_March(1-1-1970)) */
> +
> +	epoch = DAYS(year, month, day) - DAYS(1969, 11, 1);

You'd then be able to write

  epoch = days(year, month, day) - days(1970, 1, 1);

instead of the obscure chunk of code.